Indirect NO emissions from shallow groundwater in an agricultural catchment (Seine Basin, France)

Production and accumulation of nitrous oxide (NO), a major greenhouse gas, in shallow groundwater might contribute to indirect NO emissions to the atmosphere (e. g., when groundwater flows into a stream or a river). The Intergovernmental Panel on Climate Change (IPCC) has attributed an emission factor (EF) for NO, associated with nitrate leaching in groundwater and drainage ditches-0. 0025 (corresponding to 0. 25% of N leached which is emitted as NO)-although this is the subject of considerable uncertainty. We investigated and quantified the transport and fate of nitrate (NO) and dissolved nitrous oxide from crop fields to groundwater and surface water over a 2-year period (monitoring from April 2008 to April 2010) in a transect from a plateau to the river with three piezometers. In groundwater, nitrate concentrations ranged from 1. 0 to 22. 7 mg NO-N l (from 2. 8 to 37. 5 mg NO-N l in the river) and dissolved NO from 0. 2 to 101. 0 μg NO-N l (and from 0. 2 to 2. 9 μg NO-N l in the river). From these measurements, we estimated an emission factor of EF = 0. 0026 (similar to the value currently used by the IPCC) and an annual indirect NO flux from groundwater of 0. 035 kg NO-N ha year, i. e., 1. 8% of the previously measured direct NO flux from agricultural soils. © 2011 Springer Science+Business Media B.V.